1. Field of the Invention
The present invention relates to a gas-barrier laminate film having excellent gas-barrier capability, and to a method for producing it. More precisely, the invention relates to a gas-barrier laminate film favorably usable in various image display devices, in particular, to a gas-barrier laminate film useful as a substrate for flexible organic electroluminescent devices (hereinafter referred to as “organic EL devices”) and to a method for producing it, and also to an organic EL device.
2. Description of the Related Art
Heretofore, a gas-barrier laminate film fabricated by forming a thin metal oxide film of aluminium oxide, magnesium oxide or silicon oxide on the surface of a plastic substrate or a film is widely used for wrapping or packaging articles that require shielding from various gases such as water vapor or oxygen and for wrapping or packaging edibles, industrial articles and medicines for preventing them from being deteriorated. Apart from its applications for wrapping and packaging articles, in addition, the gas-barrier laminate film is being used in liquid-crystal display devices, solar cells and EL devices.
In recent development of image display devices such as liquid-crystal display devices and EL devices, the transparent substrate to constitute these devices is required to be lightweight and has a large panel size and, in addition, it is further required to satisfy high-level requirements in that it has long-term reliability and has a lot of latitude in designing its shape and that it enables curved-face display. For the transparent substrate capable of satisfying such high-level requirements, a plastic substrate is being used as a new substrate substitutable for a conventional glass substrate that is heavy and readily cracked or broken and hardly worked into a large-size panel. Not only satisfying the above requirements, but also the plastic substrate is applicable to a roll-to-roll system, and therefore it is more advantageous than a glass substrate in that the producibility with it is high and the production cost with it is low.
However, the substrate film of transparent plastics or the like is problematic in that its gas-barrier property is inferior to that of a glass substrate. When a substrate having a poor gas-barrier property is used, water vapor and air may penetrate through it; and, for example, when it is used in liquid-crystal display devices, the liquid crystal in the liquid-crystal cell may be degraded and the degraded part may be a display failure, thereby worsening the display quality of the devices. For solving the problem, a gas-barrier laminate film that comprises a thin metal oxide film formed on a substrate film has been developed. For example, as a gas-barrier laminate film for use in wrapping materials and liquid-crystal display devices, there are known a plastic film coated with silicon oxide through vapor deposition (see JP-B-53-12953, Examples), and a plastic film coated with aluminium oxide through vapor deposition (see JP-A-58-217344, Examples). These have a water-vapor barrier level of 1 g/m2·day or so.
However, in large-panel liquid-crystal display devices and high-definition display devices developed these days, the necessary gas-barrier performance of the plastic film substrate is 0.1 g/m2·day or so as the water-vapor barrier level thereof. Further recently, the development of organic EL devices and high-definition color liquid-crystal display devices that are required to have a higher gas-barrier level is being more promoted, and a transparent substrate that keeps a transparency applicable to them and has a higher gas-barrier level, especially a higher water-vapor barrier level of less than 0.1 g/m2·day is being required.
To satisfy these requirements, some methods expected to produce a higher gas-barrier level have been investigated, for example, a sputtering method of forming a thin film by the use of a plasma generated through glow discharge under low pressure, and a CVD method for film formation. In addition, also proposed is an organic light-emitting device provided with a barrier film having an alternate laminate structure of organic layer/inorganic layer fabricated according to a vacuum evaporation method (see U.S. Pat. No. 6,268,695, page 4 [2 to 5] to page 5 [4 to 49]). However, since the folding resistance of the device is unsatisfactory, the device could not be applicable to flexible image display devices.
For giving the necessary folding resistance enough for application to flexible image displays to a plastic film, disclosed is a technique of using a polymer formed through polymerization of an acrylic monomer and having a volume shrinkage of less than 10% as an organic layer of the film (see JP-A-2003-53881, page 3 [0006] to page 4 [0008]). However, this technique is problematic in that the gas-barrier property of the film is not good.
Accordingly, it is desired to develop a plastic film having both good gas-barrier property and good folding resistance on the level applicable to flexible image display devices.